What is the main gas found in the atmospheres of the gas giants?

The main gas found in the atmospheres of the gas giants—Jupiter, Saturn, Uranus, and Neptune—is hydrogen. These planets are significantly different from terrestrial planets because they lack a well-defined solid surface and are composed primarily of gases. Hydrogen is the most abundant element in the universe, making up a large portion of the composition of these giant planets.

In addition to hydrogen, helium is also present in their atmospheres, contributing to the overall gaseous envelope. However, hydrogen constitutes the majority of the atmospheric composition. The immense gravitational pull of the gas giants allows them to retain vast amounts of these lighter gases.

Other gases like oxygen and carbon dioxide are not predominant in the atmospheres of the gas giants. Instead, they are found in varying proportions in the atmospheres of terrestrial planets like Earth and Mars. Thus, understanding the predominant presence of hydrogen helps to grasp the fundamental differences between gas giants and smaller rocky planets in our solar system.